Methods and instruments for endoscopic interbody surgical techniques

ABSTRACT

This invention relates to methods and instruments for performing a surgical procedure in a disc space between adjacent vertebrae. A cannula is inserted to create a working channel through the skin and tissue of a patient using a transformational approach to the disc space. A viewing element is used to visualize working end of the cannula and the disc space. A facetectomy is performed through the working channel to access the disc space. The disc space is prepared with various instruments, such as distractors, shims, chisels and distractor-cutters that extend through the working channel. At least implant is inserted into the disc space. The procedure allows bi-lateral support of the adjacent vertebrae with the at least one implant inserted via a unitary, minimally invasive approach to disc space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/455,678, filed on Jun. 5, 2003, issuing as U.S. Pat. No. 7,320,688;which is a continuation of U.S. patent application Ser. No. 09/692,932filed on Oct. 20, 2000, and now issued as U.S. Pat. No. 6,575,899; whichclaims the benefit of the filing date of Provisional Application Ser.No. 60/160,550, filed Oct. 20, 1999. The referenced applications areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to techniques for use in interbody spinalprocedures and instruments for performing such procedures. Morespecifically, but not exclusively, the present invention relates tomethods and instruments for endoscopic interbody surgical techniques.

BACKGROUND

Normally intervertebral discs, which are located between endplates ofadjacent vertebrae, stabilize the spine and distribute forces betweenthe vertebrae and cushion vertebral bodies. The spinal discs may bedisplaced or damaged due to trauma, disease or aging. A herniated orruptured annulus fibrosis may result in nerve damage, pain, numbness,muscle weakness, and even paralysis. Furthermore, as a result of thenormal aging processes, discs dehydrate and harden, thereby reducing thedisc space height and producing instability of the spine and decreasedmobility. Most typically surgical correction of a disc space includes adiscectomy (surgical removal of a portion or all of the intervertebraldisc material.) The discectomy is often followed by fusion of theadjacent vertebrae to alleviate the pain, abnormal joint mechanics,premature development of arthritis, and nerve damage.

Traditional surgical procedures for correction of disc space pathologiescan cause significant trauma to the intervening tissues. These openprocedures often require a long incision, extensive muscle stripping,prolonged retraction of tissues, denervation and devascularization oftissue. Most of these surgeries require room time of several hours andseveral weeks of post-operative recovery time due to the use of generalanesthesia and the destruction of tissue during the surgical procedure.In some cases, these invasive procedures lead to permanent scarring andpain that can be more severe than the pain leading to the surgicalintervention.

One type of open procedure that attempts to minimize trauma to tissuethat occurs with an open procedure uses a transformational approach tothe disc space. This approach is advantageous in that it allowsplacement of one or more implants into the disc space with a singleincision. However, this approach still suffers from the drawback thatthe posterior musculature and tissue at the surgical site suffer traumaand damage due to the incision and retraction of tissue at the surgicalsite.

Minimally invasive surgical techniques are particularly desirable forspinal and neurosurgical applications because of the need for access tolocations deep within the body and the danger of damage to vitalintervening tissues. The development of percutaneous spinal procedureshas yielded a major improvement in reducing recovery time andpost-operative pain because they require minimal, if any, muscledissection and they can be performed under local anesthesia. Forexample, U.S. Pat. No. 4,545,374 to Jacobson discloses a percutaneouslumbar discectomy using a lateral approach, preferably underfluoroscopic X-ray. This procedure is limited because, among otherlimitations, it does not provide direct visualization of the discectomysite.

Other procedures have been developed which include arthroscopicvisualization of the spine and intervening structure. U.S. Pat. Nos.4,573,448 and 5,395,317 to Kambin disclose percutaneous decompression ofherniated discs with a posterolateral approach. Fragments of theherniated disc are evacuated through a cannula positioning against theannulus. The '317 Kambin patent discloses a biportal procedure whichinvolves percutaneously placing both a working cannula and avisualization cannula for an endoscope. This procedure allowssimultaneous visualization and suction, irrigation and resection in discprocedures. These approaches seek to avoid damage to soft tissuestructures and the need for bone removal through a channel. However,these approaches are limited because they do not address, for example,disc space distraction, disc space preparation and implant insertioninto the disc space. The approach of the '317 patent also requiresmultiple entries into the patient, and the approach of the '448 patentdoes not provide for direct visualization of the working space.

Further examples of instruments and methods for performing spinalsurgeries using minimally invasive approaches are found in U.S. Pat.Nos. 5,792,044 and 5,902,231 to Foley et al. The present invention isalso directed to further improvements and techniques using a minimallyinvasive approach for performing spinal surgery.

SUMMARY

One aspect of the present invention includes inserting one or moreinterbody fusion devices in a spinal disc space using a minimallyinvasive, transformational approach. Another aspect of the presentinvention includes inserting performing surgical procedures in a spinaldisc space using a minimally invasive, transformational approach.

In accordance with another aspect of the invention, a method forperforming a surgical procedure in a disc space between adjacentvertebrae is provided. The method includes inserting a cannula to createa working channel through the skin and tissue of a patient using atransformational approach to the disc space; inserting a viewing elementthrough the working channel; and preparing the disc space through theworking channel for insertion of at least one interbody fusion device.In one form, a facetectomy is performed through the working channel toaccess the disc space;

In accordance with a further aspect of the invention, a method forinserting at least one interbody fusion device in a disc space betweenadjacent vertebrae is provided. The method includes creating a workingchannel to the disc space through the skin and tissue of a patient usinga transformational approach to the disc space; preparing the disc spacethrough the working channel for bi-lateral placement of the at least onefusion device; and inserting the at least one fusion device into thedisc space through the working channel so that the adjacent vertebraeare bi-laterally supported by the at least one interbody fusion device.

In accordance with yet another aspect of the invention, a method ofrestoring disc height between adjacent vertebrae of a patient isprovided. The method includes inserting a cannula through the skin andtissue of the patient to create a working channel to the disc space;distracting the adjacent vertebrae to a disc space height with adistractor extending through the cannula into the disc space; andinserting a shim through the cannula into the disc space adjacent thedistractor. The shim has a blade with a height corresponding to thedistracted disc space height so that the blade contacts the endplates ofthe adjacent vertebrae.

In accordance with a further aspect of the invention, a method ofpreparing a disc space for insertion of an implant between adjacentvertebrae of a patient is provided. The method includes inserting acannula through the skin and tissue of the patient to create a workingchannel to the disc space; distracting the disc space to a disc spaceheight by positioning a distractor in the disc space, the distractorbeing attached to a stem that extends through the working channel, thedistractor including a body portion extending between a leading end anda trailing end, the body portion including an upper surface and anopposite lower surface and opposite first and second sidewalls extendingbetween the upper and lower surfaces, the distractor further including afirst flange and a second flange each extending proximally from theleading end of the body portion towards the trailing end, the firstflange forming a slot with the first sidewall and the second flangeforming a slot with the second sidewall; inserting a cutter through theworking channel, the cutter having an upper member with an upper cuttingedge and a lower member with a lower cutting edge and a pair of oppositesidewalls extending between the upper and lower members; and cutting theadjacent vertebrae by advancing the cutter over the body portion of thedistractor such that each sidewall of the cutter is received in arespective one of the slots.

Further objects, features, benefits, aspects and advantages of thepresent invention shall become apparent from the detailed drawings anddescriptions provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side perspective view of a cannula and viewing elementhaving application in the present invention.

FIG. 2 is a perspective view of a distractor having application in thepresent invention.

FIG. 3( a) is a top plan view of a shim having application in thepresent invention.

FIG. 3( b) is a side elevational view of the shim of FIG. 3( a).

FIG. 4( a) is a top plan view a driver for the shim of FIG. 3( a).

FIG. 4( b) is a side elevational view of the driver of FIG. 4( a).

FIG. 4( c) is an end view of the driver of FIG. 4( a).

FIG. 5( a) is a perspective view of one embodiment of a chisel havingapplication in the present invention.

FIG. 5( b) is an enlarged perspective view of the cutting head of thechisel of FIG. 5( a).

FIG. 6( a) is a perspective view of one embodiment of another chiselhaving application in the present invention.

FIG. 6( b) is an enlarged perspective view of the cutting head of thechisel of FIG. 6( a).

FIG. 7( a) is a perspective view of a distractor-cutter assemblyaccording to a further aspect of the present invention.

FIG. 7( b) is a sectional view taken through line 7(b)-7(b) of FIG. 7(a).

FIG. 7( c) is an enlarged top plan view of the distal end portion of thedistractor-cutter assembly of FIG. 7( a).

FIG. 7( d) is an enlarged side elevation view of the distal end portionof the distractor-cutter assembly of FIG. 7( a).

FIG. 8 is a perspective view of a slap hammer having application withthe present invention.

FIG. 9 is a perspective view of an implant holder and implant havingapplication with the present invention.

FIGS. 10( a)-(h) depict the steps of various methods of accessing thedisc space according to the present invention.

FIGS. 11( a)-(h) depict the steps of a method for preparing a disc spacefor insertion of interbody fusion device into a disc space.

FIG. 12 is a plan view of a disc space illustrating bi-lateralpositioning of interbody fusion devices in the disc space.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

For the purposes of promoting an understanding of the principles of thepresent invention, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is intended thereby. Any alterations andfurther modification in the described processes, systems, or devices,and any further applications of the principles of the invention asdescribed herein are contemplated as would normally occur to one skilledin the art to which the invention relates.

Aspects of the present invention have application to a wide range ofsurgical procedures, and particularly spinal procedures such aslaminotomy, laminectomy, foramenotomy, facetectomy and discectomy, usinga posterior, postero-lateral, or a lateral approach to the disc space.The devices and instruments of present invention have application toinventive surgical techniques that permit each of these several types ofsurgical procedures to be performed via a single working channel. Thepresent invention also has application to surgical techniques forpreparing a disc space for insertion of an implant into the disc space.The present invention further has application in a transformational,minimally invasive surgical procedure in which the disc space isprepared for insertion of one or more implants into the disc space witha unilateral approach.

Referring now to FIG. 1, one example of a cannula assembly 15 forproviding an endoscopic, minimally invasive approach to disc space isprovided. It should be understood that other shapes for cannula assembly15 are also contemplated herein, so long as the cannula assemblyincludes a protective sleeve for providing a minimally invasive approachto the disc space and visualization of the surgical site. Cannulaassembly 15 includes a cannula 20 defining a working channel 25 betweena working end 21 and a proximal second end 22. The length of cannula 20is sized so that second end 22 is positioned above the skin of thepatient when cannula 20 is positioned at the surgical site.

Cannula assembly 15 also includes an endoscope assembly 30 mountable oncannula 20. Endoscope assembly 30 includes an upper end 31 having aviewing apparatus 32, such as an eyepiece, an illumination element 38,and an elongated viewing element 34 disposed within the working channel25. Viewing element 34 has a distal end 34 a positionable adjacent thedistal working end 21 of cannula 20. The particular viewing element usedis not critical to the invention. Any suitable viewing element iscontemplated that allows visualization of the surgical site iscontemplated. In the illustrated embodiment, distal end 34 a of viewingelement 34 is extendable from and retractable into cannula 20. Viewingelement 34 is further rotatable about and positionable at variouslocations around the working channel 25. In one embodiment, theelongated viewing element 30 includes a fiber optic scope and a lens atthe distal end 34 a. The fiber optic scope includes illumination fibersand image transmission fibers (not shown). Alternatively, the viewingelement may be a rigid endoscope, or an endoscope having a steerable orbendable tip.

Cannula assembly 15 contemplates any configuration or apparatus allowingthe optics to be supported adjacent the working channel 25. In theembodiment shown in FIG. 1, a fixture 33 is provided for mountingendoscope assembly 30 on cannula 20 with elongated viewing element 34disposed in working channel 25 of cannula 20. Fixture 33 includes aclamp 35 attachable to the second end 22 of cannula 20. Clamp 35 isclamped on outer surface 23 of cannula and maintains the opening forworking channel 25 at proximal end 22. The working channel 25 is sizedto receive one or more surgical tools therethrough for performingsurgical procedures through cannula 20.

Cannula assembly 15 may also include irrigation and aspirationcomponents 16 and 17 extending along viewing element 34 in cannula 20.Endoscope assembly 30 includes a detachable endoscope 36 that isremovable from clamp 35. One type of modular endoscope assemblycontemplated by the present invention is described in U.S. patentapplication Ser. No. 09/160,882, filed Sep. 25, 1998, which applicationis incorporated herein by reference in its entirety. Cannulas andendoscope assemblies are also described in U.S. Pat. Nos. 5,792,044 and5,902,231 to Foley et al., which patents are also incorporated herein byreference in their entirety.

The present invention also contemplates instruments for use with thecannula assembly 15 to prepare a disc space for insertion of one or moreimplants and inserting the implants in the disc space. Specificinstruments include distractors, shims, chisels, distractor-cutters,implant holders, reamers, and drills. Other instruments for performingsurgical procedures on the vertebral bodies or in the disc space arealso contemplated herein as would occur to those skilled in the art solong as the instruments are capable of being used in a minimallyinvasive procedure through working channel 25 of cannula 20.

In FIG. 2, a distractor 40 for distracting a disc space is provided.Distractor 40 includes a shaft 44 extending between a proximal end 42and a distal end 43. Shaft 44 has a length sufficient to extend throughcannula 20 with proximal end 42 disposed outside proximal end 22 ofcannula 20. A head 46 extends from distal end 43. Head 46 is shown asintegrally formed with shaft 44, but it is also contemplated that head46 may be detachable via, for example, a threaded connection with shaft44. Head 46 has a height h between support surfaces 46 a and 46 b thatcorresponds to the desired height for the distracted disc space.Proximal end 42 can be connected to a driving tool, such as a slaphammer or the like, to facilitate insertion. One example of a slaphammer is described hereinbelow with respect to FIG. 8. Distractor 40may also be inserted by the surgeon by hand into the disc space.

It is contemplated that distractor 40 is inserted into the disc spacesupport surface 46 a and 46 b transverse to the vertebral end plates,and distractor 40 is rotated to rotate head 46 so that support surfaces46 a and 46 b contact a respective one of the vertebral endplates. It isalso contemplated that a wrench or other tool configured to impart arotational force to distractor 40 to rotate head 46 in the disc spacecan be connected at proximal end 42. It is further contemplated that anumber of distractors 40 may be provided with varying heights h forsequential distraction of the disc space to the desired disc spaceheight. The depth of insertion of blade 54 can be monitored under directvision using viewing element 30. Also contemplated are x-ray imaging orimage-guided navigation techniques that allow visualization ofdistractor 40 in the disc space. Instruments and techniques forimage-guided navigation are further discussed in U.S. Pat. No. 6,021,343to Foley et al. and also in PCT Application Serial No. PCT/US/95/12984(Publication No. WO/96/11624) to Buchholz et al; each of which isincorporated herein by reference in its entirety.

Referring now to FIGS. 3( a) and 3(b), a shim 50 for maintainingdistraction of a distracted disc space is provided. Shim 50 isextendable through cannula 20 to maintain distraction of a disc spacedistracted with distractor 40. Shim 50 includes a shaft 52 of sufficientlength to extend through cannula 20 connected to a blade 54. Blade 54has a first side surface 55 a and a second side surface 55 b. Whileblade 54 is shown as a flat blade, it is contemplated that any of avariety of blade shapes may be utilized in conjunction with shaft 52 ofthe present invention. Shaft 52 extends to proximal end 56. Shaft 52 hasopposite side surface 53 a and 53 b that are co-planar with sidesurfaces 55 a and 55 b, respectively, of blade 54. Shaft 52 preferablyis made from a material and has a configuration that allows shaft 52 tobe bent away from axis A as needed to provide clearance for the surgeonto access the operative site through cannula 20.

Blade 54 has top surface 54 a for contacting the superior vertebralendplate in the disc space and bottom surface 54 b for contacting theinferior vertebral endplate in the disc space. Blade 54 has a leadingend 60 extending between top surface 54 a and bottom surface 54 b.Preferably, leading end 60 is rounded to facilitate insertion of blade54 into the disc space. Blade 54 also includes a pair of shoulders 62 aand 62 b. One shoulder 62 a extends between shaft 52 and top surface 54a, and the other shoulder 62 b extends between shaft 52 and bottomsurface 54 b. When blade 54 is inserted into the disc space, sidesurfaces 55 a, 55 b protect the disc space and prevent migration oftissue and other anatomical material laterally into the disc spaceduring subsequent surgical procedures.

Blade 54 has a length 1 extending between leading end 60 and shoulders62 a, 62 b. Preferably, length 1 is selected based on the depth of thedisc space and the desired insertion depth of blade 54. Blade 54 alsohas a height h1 between top surface 54 a and bottom surface 54 b. Heighth1 is preferably selected based on the height of the distracted discspace after it has been finally distracted with distractor 40. Blade 54has a thickness t2 measured between first side surface 55 a and secondside surface 55 b. It is contemplated that ratio of height h1 tothickness t1 is greater than about 2.0. In a most preferred form, thisratio is greater than about 5.0. Shaft 52 has a height h2, and athickness t2 that preferably corresponds to blade thickness t1. However,it is also contemplated herein that thickness t1 and t2 have differentvalues. It is preferred that height h1 of blade 54 is greater thanheight h2 of shaft 52.

In a specific embodiment of shim 50, blade 54 has thickness t1 of about1.5 millimeters. Height h1 for the smallest sized blade 54 is 8.0millimeters, and additional larger heights h1 are provided in incrementsof 2 millimeters. The shaft 52 in this specific embodiment has a heighth2 of 6.0 millimeters and a thickness t2 of about 1.5 millimeters. Shim50 is made from aluminum or other material that allows shaft 52 to bebent by the surgeon and maintained in the bent condition during surgeryto effectively move the shaft out of the visual field.

Referring now to FIGS. 4( a)-4(c), a driver 70 for impacting or drivingthe shim 50 into the disc space is provided. Driver 70 includes achannel 72 and a handle 74 extending between a distal end 73 and aproximal end 76. Channel 72 is attached or formed at distal end 73 ofhandle 74 and extends distally therefrom. Driver 70 is particularlysuited for use with shim 50 through cannula 20 because channel 72 isend-loaded over proximal end 56 of shaft 52. Preferably, channel 72 isoffset from the handle 74, as shown in FIG. 4( b), to facilitateinsertion of shaft 52 into channel 72 and manipulation of driver 70 withrespect to shim 50.

Channel 72 has a wall 80 that extends therearound. Channel 72 hasopposite end openings 78, 79 and a receptacle 73 defined by wall 80 thatextends along the length of channel 72. Receptacle 73 is sized toslidably receive shaft 52 of shim 50 therein. Channel 72 includes adriving end 77 configured to contact shoulders 62 a, 62 b of shim 50,delivering the driving force at blade 54 without impacting shaft 52.

Use of driver 70 will now be described with respect to shim 50. Blade 54is positioned at the desired insertion location adjacent the distracteddisc space. The channel 72 is then end-loaded onto shaft 52 by placingopening 78 over proximal end 56. Driver 70 is slid along shaft 52 untildriving end 77 is positioned adjacent blade 54. It is contemplated thata driving force can be provided to insert blade 54 into the disc spaceby withdrawing driver 70 a short distance away from shoulders 62 a, 62b, and then applying a downward force so that driving end 77 impacts theshoulders 62 a, 62 b. This is repeated until blade 54 is inserted to thedesired depth in the disc space. It is also contemplated that thedriving force may be applied through driver 70 via a hammer or otherdevice impacting driver 70. The depth of insertion of blade 54 can bemonitored under direct vision using viewing element 30. Alsocontemplated are x-ray imaging or image-guided navigation techniquesthat allow visualization of blade 54 in the disc space. Thus, it ispreferred that blade 54 be radiolucent.

A box chisel for preparation of a preformed cavity in the intervertebraldisc space is depicted in FIGS. 5( a) and 5(b). Box chisel 90 includes ahandle 92, having an engagement hole 93 adapted for attachment of animpacting tool such as a slap hammer or the like. It is alsocontemplated that chisel 90 can be manipulated by hand to form a cavityin the disc space. Box chisel 90 includes shaft 94 extending from handle92 and connecting with cutting head 96. Shaft 94 defines a longitudinalaxis 91 and has a length sufficient to extend through cannula 20.Cutting head 96 includes first arm 97 and opposing second arm 99extending from shaft 94 substantially parallel to longitudinal axis 91.Upper cutting blade 98 and opposing lower cutting blade 100 are disposedbetween first and second arms 97 and 99. First arm 97 and second arm 99define internal cavity 106 for receipt of bone chips and cutting debris.One or both of first arm 97 and second arm 99 include index markings104, which indicate the depth of cut for the box chisel, thus allowingthe surgeon to determine the depth of cut into the intervertebral space.

Non-cutting extension 103 is attached to first arm 97. Similarly,non-cutting extension 102 is attached to first arm 99. Non-cuttingextensions 103 and 102 are positioned to extend distally beyond cuttingblades 98 and 100 in a direction parallel to the longitudinal axis.Non-cutting extension 103 includes an upper guide surface 103 a and alower guide surface 103 b extending at least partially distally beyondthe cutting edges. Similarly, non-cutting extension 102 includesidentical upper and lower guiding surfaces 102 a and 102 b. The guidingportions contact the surface of the adjacent vertebral endplates priorto cutting blades 98 and 100. Preferably non-cutting extensions 103 and102 are rounded and follow the interior surfaces of the opposing endplates of adjacent vertebrae to center cutting blades 98 and 100 in thedisc space between the two end plates. When the two cutting blades arecentered between the opposing endplates, the blades generally cut equalamounts of bone from each end plate and are prevented from creating apotential offset opening between the endplates, resulting in improperimplant placement and excess bone removal, which could increase the riskof implant interface subsidence.

Another embodiment of a chisel according to the present invention iscurved chisel 110 depicted in FIGS. 6( a) and 6(b). Curved chisel 110 isfor preparing a curved preformed cavity in the intervertebral discspace, and is particularly adapted for preparing a disc space forbi-lateral placement of implants in the disc space via a unitarytransformational approach. Curved chisel 110 includes a handle 112,having an engagement hole 113 adapted for attachment of an impactingtool such as a slap hammer or the like. In addition, chisel 110 includesshaft 114 extending from handle 112 and connecting with cutting head116. Shaft 114 defines a curvilinear longitudinal axis 111 having aradius of curvature R along a portion of its length. Radius R isprovided such that chisel 110 may be inserted through the cannula 20 yetdefine a properly positioned and aligned cavity in the disc space.Cutting head 116 includes first arm 117 and opposing second arm 119extending from shaft 114 substantially parallel to longitudinal axis111. Upper cutting blade 118 and opposing lower cutting blade 120 aredisposed between first and second arms 117 and 119. First arm 117 andsecond arm 119 define internal cavity 126 for holding bone chips andcutting debris passed rearwardly from cutting head 116.

Non-cutting extension 123 is attached to first arm 117. Similarly,non-cutting extension 122 is attached to first arm 119. Non-cuttingextensions 123 and 122 are positioned to extend distally beyond cuttingblades 118 and 120 in a direction parallel to the longitudinal axis.Non-cutting extension 123 includes an upper guide surface 123 a and alower guide surface 123 b extending at least partially distally beyondthe cutting edges. Similarly, non-cutting extension 122 includes upperand lower guiding surfaces 122 a and 122 b. The guiding surfaces contactthe vertebral endplates prior to cutting blades 118 and 120. Preferablynon-cutting extensions 123 and 122 are rounded and follow the interiorsurfaces of the opposing end plates of adjacent vertebrae to centercutting blades 118 and 120 in the disc space between the two end plates.When the two cutting blades are centered between the opposing endplates,the blades cut equal amounts of bone from each end plate and areprevented from creating a potential offset opening between theendplates, resulting in improper implant placement and excess boneremoval, which could increase the risk of implant interface subsidence.

In use chisels 90, 110 are positioned through cannula 20 with viewingelement 30 connected thereto. Cutting heads 96, 116 are positioned insubstantial alignment with a disc space between adjacent vertebralendplates under direct vision. Non-cutting edges are inserted into thedisc space with the guide surfaces of extensions 102, 103 of chisel 90or guide surfaces of extensions 122, 123 of chisel 110 contacting thevertebral endplates. Cutting head 96, 116 is then advanced, by hand orby use of a slap hammer if necessary, with blades 98, 100 of chisel 90or blades 118, 120 of chisel 110 removing the tissue of the vertebralendplates along the path of insertion. The depth of insertion of chisels90, 110 can be monitored under direct vision, image-guided navigationinstruments, with a viewing element inserted in the disc space, or viax-ray or fluoroscopic imaging

A distractor-cutter instrument is described hereinbelow and also in U.S.patent application Ser. No. 09/692,980; entitled METHODS AND INSTRUMENTSFOR INTERBODY SURGICAL TECHNIQUES, filed Oct. 20, 2000, whichapplication is incorporated herein by reference in its entirety.Referring now further to FIGS. 7( a)-7(d), there is shown a distractorassembly 210 that includes a distractor 218 at the distal end of stem216. At the proximal end of stem 216 is a coupling 214 for securinghandle 212 to stem 216. Distractor 218 includes a body portion 220extending between leading end 222 and trailing end 224. A first flange226 and a second flange 228 are secured to body portion 220 at leadingend 222, and extend from leading end 222 towards trailing end 224. It ispreferred that flanges 226, 228 are integrally formed with body portion220 at leading end 222. In the illustrated embodiment, a first end wall246 extends between leading end 222 and first flange 226 and a secondend wall 248 extends between leading end 222 and second flange 228.However, flanges 226, 228 could also be removably attached to bodyportion 220.

Body portion 220 has first sidewall 230 and an opposite second sidewall232. Each of the sidewalls 230, 232 extend towards the adjacentvertebrae between an upper surface 234 and an opposite lower surface 236of body portion 220. A first slot 242 is formed between first flange 226and first sidewall 230. A second slot 244 is formed between secondflange 228 and second sidewall 232. Slots 242 and 244 have a width “d”sized to accommodate the distal end of a cutting instrument 252, asdiscussed further below.

Body portion 220 further includes a cavity 238 formed therethroughextending between upper surface 234 and the opposite lower surface. Bodyportion 220 has a height H1 between upper surface 234 and lower surface236 that corresponds to the desired height for the distracted discspace. In the illustrated embodiment, the leading end portion of bodyportion 220 tapers to a reduced height H2 between upper surface 234 andlower surface 236 at leading end 222 to facilitate insertion ofdistractor 218 into the disc space. Preferably, flanges 226, 228 have aheight that is equal to or is less than height H1 of body portion 220,and have a tapered portion that corresponds to the taper of body portion220 towards leading end 222. The depth of insertion of distractor 218into the disc space can be monitored under direct vision, image-guidednavigation instruments, with a viewing element inserted in the discspace, or via x-ray or fluoroscopic imaging of distractor 218.

According to a further aspect of the invention a cutting instrument orcutter 252 is provided that cooperates with distractor 218 to form aspinal instrument assembly 250. Spinal instrument assembly 250 providesfor distraction of the adjacent vertebrae and for cutting material fromthe disc space and/or the adjacent vertebrae to form an implantinsertion location. Cutter 252 includes a shaft 264 and a cutting head253 at the distal end of shaft 264. Shaft 264 includes a first sidewall258 and an opposite sidewall 260. Sidewalls 258 and 260 are connected byan upper member 254 and an opposite lower member 256. Upper member 254includes an upper cutting edge 254 a at its distal end and lower member256 includes a lower cutting edge 256 a at its distal end. While theillustrated embodiment has shaft 264 with a square cross-sectionalshape, other shapes are also contemplated, including, for example, acircular or rectangular cross-section.

Shaft 264 includes an interior channel 262 formed therethrough thatopens at the distal end of cutter 252. As shown in FIG. 7( b), channel262 has a distal first portion 262 a sized to receive stem 216 and bodyportion 220 of distractor assembly 210 with handle 212 removed from stem216. Preferably, first portion 262 a has a size slightly larger thanbody portion 220 and a shape approximating the shape of body portion220. This provides a slip fit between body portion 220 and cutting head253 that will guide cutting head 253 into the disc space and into thebony material of the adjacent vertebral bodies. Although thecross-section of the remaining proximal portion of channel 262 can haveany shape, it is contemplated that the entire length of channel 262 hasa shape that corresponds to the shape of first portion 262 a.

Upper member 254 includes an opening 268 and lower member 256 includesan opening 270 identical to opening 268. These openings aresubstantially alignable with cavity 238 of distractor 218, andfacilitate the removal of cut material from cavity 238 when instrumentassembly is withdrawn from the disc space after cutting bony material.Cutter sidewall 260 includes a recess 272 formed therein, and cuttersidewall 258 includes a similarly shaped recess (not shown.) Therecesses allow cutting edges 254 a and 256 a to be advanced beyond theleading end 222 of distractor 218. End walls 246, 248 prevent cuttinghead 253 from being advanced too far beyond leading end 222 of bodyportion 220.

Sidewall 260 includes a window 280 to further provide visual observationand/or confirmation of the position of cutting head 253 with respect todistractor 218 by enabling viewing of depth markings on stem 216 ofdistractor assembly 210. Shaft 264 further includes a probe 274 forimage guided navigation adjacent its proximal end to provide control andmonitoring of cutter 252. Further details regarding probe 274 areprovided in U.S. Pat. No. 6,021,343 to Foley et al. Also contemplatedare the use of x-ray and fluoroscopic imaging techniques to visualizecutting head 253 as it is inserted in the disc space.

Head 246 has a height H3 that corresponds to the desired height of theprepared disc space into which the implant is to be inserted. It iscontemplated that cutter 252 is inserted into the disc space with uppermember 254 and lower member 256 parallel to the vertebral end plates andguided by body portion 220 of distractor 218. It is further contemplatedthat a number of cutters 252 of increasing height H3 may be provided andsequentially inserted over distractor 218 for removal of bony materialfrom the vertebral endplates. A standard coupling 76 is provided at theproximal end of cutter 252 for attachment to a cutter handle 278 tofacilitate gripping and control of cutter 252. The proximal end ofcutter 252 can also be connected to or contacted by a driving tool, suchas a slap hammer or the like to drive the cutting edges 254 a, 256 ainto the bony material.

FIG. 8 shows one example of a slap hammer engageable to attachment hole93 of box chisel 90, to attachment hole 113 of chisel 110, to cutter252, to distractor assembly 210 or implant holder 130 (FIG. 9.) Slaphammer 150 includes handle 152 and a shaft 154 extending to an oppositethreaded end 155. Threaded end 155 threadedly engages internal threadsin holes 93, 113. Slap hammer 150 includes weight 156 that slides alongshaft 154. Slap hammer 150 allows for controlled force when impactingthe connected instrument. The slap hammer also provides a means forremoval of impacted surgical tools from the disc space.

Referring now to FIG. 9, an embodiment of an implant holder 130 and aninterbody fusion device, such as implant I, are illustrated. The implantholder 130 includes a shaft 132 extending between a handle 136 anddistal end 133. Shaft 132 has a length sufficient to extend throughcannula 20. Implant holder 130 releasably secures an implant forinsertion into a preformed cavity in the disc space under direct visionwith viewing element 30. Distal end 133 includes threaded extension 135threadedly received within an internally threaded opening in implant Iin order to engages implant holder 130 thereto. Handle 136 includes aproximal end 137 that may be impacted in order to insert the implant inthe disc space. In one embodiment, proximal end 137 includes internallythreaded opening 138 configured to engage slap hammer 150. The surgeonmay also insert implant I into the disc space by hand using handle 136.In addition to the visualization techniques described herein or thoseknown in the art, an adjustable depth stop 134 may be provided on shaft132 to control the depth of insertion of implant I into the disc space.Once implant I has been driven into the disc space, the implant isreleased from implant holder 130.

Implant I may be any device suitable for insertion into the disc spacethrough cannula 20. Use of implants that restore the disc height,restore segmental alignment and balance, protect nerve roots, restoreweight bearing to anterior surfaces, and immobilize the unstabledegenerated intervertebral disc area are contemplated. The implantsinserted with the techniques of the present invention may beconveniently implanted using the instruments and tools of the presentinvention to prepare the disc space and any instrument that will firmlyhold implant I and permit insertion in the disc space through cannula 20is also contemplated.

Implant I can be a spacer or interbody fusion device. Implant I may havean oblong cross-section, as shown in FIG. 9, or have a cross-sectionthat is circular, oval, square, trapezoidal or rectangular. Implant Imay be sized such that a single implant I is inserted in the disc space,or may have a size so that two or more implants can be inserted andbi-laterally positioned in the disc space. Examples implants I in theform of an interbody fusion devices are described in U.S. Pat. No.5,897,556 which is incorporated herein by reference. Other examples ofsuitable interbody fusion devices are described in ProvisionalApplication Ser. No. 60/160,506 filed on Oct. 20, 1999, whichapplication is incorporated herein by reference in its entirety. In yetanother example, a banana-shaped implant is inserted in to the discspace. An example of such a banana-shaped implant is disclosed inProvisional Application Ser. No. 60/160,667 filed on Oct. 21, 1999,which application is incorporated herein by reference in its entirety.

It is preferred that the interbody fusion devices inserted into the discspace have a hollow interior forming a chamber or depot for osteogenicor bone-growth material G (FIG. 12.) The device can be packed withosteogenic material prior to implantation in the disc space, or theosteogenic material may be inserted into the chamber or depot after oneor more of the devices have been inserted. In a preferred embodiment,the osteogenic composition substantially fills the hollow interiordefined by the devices to promote fusion and bone growth between theadjacent vertebrae. It is also contemplated that osteogenic or bonegrowth material may be packed around the device(s) in the disc space.

Any suitable osteogenic material or composition is contemplated,including autograft, allograft, xenograft, demineralized bone, andsynthetic and natural bone graft substitutes, such as bioceramics andpolymers, and osteoinductive factors. The terms osteogenic material orosteogenic composition used herein broadly include any material thatpromotes bone growth or healing including autograft, allograft,xenograft, bone graft substitutes and natural, synthetic and recombinantproteins, hormones and the like.

The steps of the spinal surgical procedure in accordance with one aspectof the present invention are depicted in FIGS. 10( a)-10(h). As can bediscerned from each of the depicted steps (a)-(h), the present inventioncontemplates a transformational approach to the disc space, as indicatedby cannula 20. The following surgical steps also have application withother approaches to the spine, such as the medial posterior approachindicated by cannula 20′, or other posterior, postero-lateral andanterior approaches. In the discussion that follows, reference willgenerally be made to a transformational approach.

In a first step of the technique, a guidewire 170 can be advancedthrough the skin and tissue into the facet joint of a vertebral body V.A small incision can be made in the skin to facilitate penetration ofguidewire 170 through the skin. In addition, the guidewire, which may bea K-wire, can be inserted under radiographic or image guided control toverify its proper positioning on the vertebra V. The positioning of theguidewire is dependent upon the surgical procedure to be conductedthrough the working channel cannula of the present invention.Preferably, the guidewire 170 is solidly anchored into the vertebralbone, being tapped by a mallet if necessary.

In subsequent steps of the preferred method, a series of tissue dilatorsare advanced over the guidewire 170, as depicted in FIGS. 10( b)-10(d).Alternatively, the dilators can be advanced through the incision withoutthe aid of a guidewire, followed by blunt dissection of the underlyingtissues. In the specific illustrated embodiment, a series ofsuccessively larger dilators 171, 172 and 173 are concentricallydisposed over each other and over the guidewire 170 and advanced intothe body to sequentially dilate the soft tissues. In a specificembodiment, the dilators have successively larger diameters, with sizesthat increase from the smallest to the largest dilator depending uponthe anatomical approach and upon the desired size of the working channelfor cannula 20.

In the next step of the illustrated technique, the working channelcannula 20 is advanced over the largest dilator 173, as shown in FIG.10( e), and the dilators and guidewire 170 are removed, as shown in FIG.10( f). Preferably, the working channel cannula 20 has an inner diametersuch that it can be easily advanced over the outer diameter of the largedilator 173. Cannulas having various sized working channels arecontemplated depending upon the anatomical region and surgicalprocedure.

With the cannula 20 in position, a working channel is formed between theskin of the patient to a working space adjacent the spine. It isunderstood that the length of the cannula 20 is determined by theparticular surgical operation being performed and the anatomysurrounding the working space. For instance, in the lumbar spine thepatient requires a longer cannula 20 than a similar procedure performedin the cervical spine where the vertebral body is generally closer tothe skin.

In accordance with the present surgical technique, the working channelcannula 20 is at least initially only supported by the soft tissue andskin of the patient. Thus, in one aspect of the preferred embodiment,the cannula 20 can include a mounting bracket 27 affixed to the outersurface of the cannula (FIG. 10( f)). This mounting bracket 27 can befastened to a table-based flexible support arm 160, which can be ofknown design. Preferably, the flexible support arm 160 is engaged to thebracket 27 by way of a bolt and wing nut 161, as shown in FIG. 10( h),although other fasteners are also contemplated. This flexible arm 160can be mounted to the surgical table and can be readily adjusted into afixed position to provide firm support for the cannula 20. The flexiblearm 160 preferably may be contoured as required to stay clear of thesurgical site and to allow the surgeons adequate room to manipulate thevariety of tools that would be used throughout the procedure. Returningto FIG. 10( g), once the cannula 20 is seated within the patient,endoscope assembly 30 can be engaged over the proximal end of thecannula 20. Endoscope assembly 30, as shown in FIG. 1 and describedabove, provides an endoscope with an elongated viewing element, such aselement 34 in FIG. 1, that extends through cannula 20 adjacent theworking channel.

With the endoscope assembly 30 supported by cannula 20, the surgeon candirectly visualize the area beneath the working channel 25 of thecannula 20. The surgeon can freely manipulate the viewing element 34within the working channel 25 or beyond the distal end of the cannulainto the working space. In the case of a steerable tip scope, the secondend 34 a of viewing element 30, which carries the lens, can bemanipulated to different positions. With virtually any type of viewingelement, the manipulation and positioning of the scope is not limited bythe procedure to be performed. For instance, variety of rongeurs,curettes, trephines, distractors, distractor-cutters, chisels, shims,and implant holders can be extended through working channel 25 ofcannula 20 (see FIG. 1) into the working space. It is understood thatthese various tools and instruments are designed to fit through theworking channel. The present invention is not limited to particularsizes for the working channel and effective diameter, since thedimensions of the components will depend upon the anatomy of thesurgical site and the type of procedure being performed.

One important feature of the present invention is achieved by the largediameter of the working channel 25 in the cannula 20. This largediameter allows the surgeon or surgeons conducting the surgicalprocedure to introduce a plurality of instruments or tools into theworking space. For example, as described above, a distractor and a shim,a chisel and a shim, a distractor-cutter or a distractor-cutter and ashim, or an implant and a shim could be extended together through theworking channel. Likewise, the present invention contemplates thesimultaneous introduction of other types of instruments or tools as maybe dictated by the particular surgical procedure to be performed. Forexample, discectomy instruments could be inserted through channel 25,such as a trephine for boring a hole through the disc annulus and apowered tissue cutter for excising the herniated disc nucleus. Anappropriately sized curette and a rongeur may be simultaneously extendedthrough the working channel into the working space. Since all operationsbeing conducted in the working space are under direct visualizationthrough the viewing element, the surgeon can readily manipulate each ofthe instruments to perform tissue removal and bone cutting operations,without having to remove one tool and insert the other. Furthermore,aspects of the invention which permit a wide range of motion to theviewing element allow the surgeon to clearly visualize the target tissueand clearly observe the surgical procedures being conducted in theworking space.

The surgeon can capitalize on the same advantages in conducting a widerange of procedures at a wide range of locations in the human body. Forexample, a facetectomy could be conducted through the working channel bysimply orienting the working channel cannula 20 over the particularfacet joints. The devices can also be used to prepare a site for fusionof two adjacent vertebrae, and for implantation of a fusion device ormaterial.

For example, one surgical technique will now be described with referenceto FIGS. 11( a)-11(h). Those skilled in the art will understand theFIGS. 11( a)-11(h) demonstrate a transformational approach to the discspace that requires removal of the facet joint to provide access to thedisc space in an oblique orientation relative to the midline of thevertebral bodies. This approach allows disc space preparation andinsertion of one or more implants bilaterally into the disc space via aunitary approach to the disc space.

An incision can be made in the skin posterior to a particular disc spaceto be fused. As the tissue beneath the skin is successively excised orretracted, the working channel cannula 20 can be progressively advancedtoward the anticipated working space adjacent the vertebral disc andsecured with flexible arm 160, as shown in FIGS. 10( a)-10(h). Endoscopeassembly 30 is then mounted on cannula 20, and the remaining steps ofthe procedure can be performed under direct vision from viewing element34. A portion of the facet joints of the adjacent vertebral bodies areresected through cannula 20, and a discectomy is performed throughcannula 20. Typically, this preparation includes preparing an opening inthe disc annulus, and excising all, or preferably as part, of the discnucleus through this opening. If a partial discectomy is performed,enough material is removed to allow insertion of the distractor.

In subsequent steps, the disc space is distracted to the desired discspace height. As shown in FIG. 11( a) distractor 40 is inserted throughcannula 20 into the disc space. The disc space is distracted withdistractor 40 by rotating head 46 ninety degrees in the disc space, asshown in FIG. 11( b). The disc space can be sequentially distracteduntil the desired disc space height is obtained. To sequentiallydistract the disc space, shim 50 is inserted into the disc spaceadjacent distractor 40, as shown in FIG. 11( c), to maintain thedistracted disc space height after removal of distractor 40. Preferably,driver 70 is used to drive shim 50 to the desired depth. If necessary,the first distractor is removed and a next larger distractor 40 isinserted into the disc space, and the first shim removed. Another shim50 corresponding to the next larger distractor height is then insertedas described above. When the desired disc space distraction has beenachieved, the final distractor is removed from the disc space, and discspace preparation continues adjacent shim 50 that remains in the discspace. In addition to maintaining distraction of the disc space, shim 50also shields the disc space and helps prevent migration of nerves andtissue into the working space. The bendable shaft of shim 50 can be bentover the proximal end of cannula 20 to provide clear access to workingchannel 25. A complete discectomy, if necessary, can now be completedwhile the shim supports the disc space in an open position.

As shown in FIG. 11( d), it is contemplated that one type of instrumentthat could be inserted through working channel 25 of cannula 20 tocomplete the discectomy is a rotate cutter 310, such as the rotatecutter described in U.S. patent application Ser. No. 09/181,353, whichis incorporated herein by reference in its entirety. The rotate cutter310 has a head 312 inserted alongside the shim and rotated by a shaft314 once or twice to remove residual disc material and osteophytes atthe dorsal-most endplate. Blades 316, 318 cut the disc material anddeposit it in trough 320 between blades 316, 318 for removal from thedisc space. Removal of osteophytes facilitates placement of the chisel90, 110 in the disc space. Sequentially larger rotate cutters can beinserted to remove disc material safely.

As shown in FIGS. 11( e) and 11(f), box chisel 90 or curved chisel 110is next used to form an insertion location for one or more implants,depending on the patient anatomy and desired positions of the one ormore implants. Chisel 90, 110 are inserted through cannula 20 to cut theendplates of the adjacent vertebrae to form a cavity or trac for implantinsertion while shim 50 maintains disc space distraction. If necessary,cannula 20 can be manipulated through the skin and tissue to providedifferent cutting angles with respect to the disc space for further boneremoval. After removal of the chisel 90, 110 the discectomy rongeur andother instruments can be inserted through cannula 20 to remove anyresidual soft tissue and bone material.

As shown in FIG. 11( g), distractor-cutter 250 can be used in additionto or as an alternative distractor 40 and chisel 90. Distractor 218 ofdistractor assembly 210 is inserted into disc space D through workingchannel 25 of cannula 20 to distract disc space to the desired heightbetween the adjacent vertebrae. It is contemplated that, if necessary,the disc space can be sequentially distracted before insertion ofdistractor 218 or sequentially distracted by a number of distractors 218of increasing height H1 until the desired disc space height is obtained.

When the desired distraction has been achieved, handle 212 is removedfrom the proximal end of stem 216 and cutter 252 is slid over theproximal end of stem 216 to position cutting head 253 adjacent the discspace and distractor 218. Cutter 252 is advanced over body portion 220of distractor 218 so that the bony material of the vertebral endplatesis cut by cutting edges 254 a and 256 a. At least a portion of the cutmaterial is deposited in cavity 238 of distractor 218. Cutter 252 formsa path or trac for implant insertion while distractor 218 maintains discspace distraction. If necessary, cannula 20 can be manipulated throughthe skin and tissue to provide different cutting angles with respect tothe disc space for further bone removal. Flanges 226, 228 protect theadjacent vasculature and nerves as cutter 252 advances over body portion220, and body portion 218 guides the cutting edges to provide a uniformand controlled depth of cut and bone removal of the adjacent vertebralbodies.

Implant I, preferably a fusion device, bone dowel, push-in implant,threaded implant or the like, can then be advanced through the workingchannel 25 of cannula 20 and into the prepared cavity or trac at thesubject disc space via implant holder 130. The depth of insertion can becontrolled via depth stop 134. The implant I of FIG. 11( h) iselongated, and provides bi-lateral support of the vertebral bodies. Itis also contemplated that more than one implant can be inserted into thedisc space, as shown in FIG. 12. The first interbody fusion device 162is positioned at a first bi-lateral location in the disc space oppositecannula 20. A second interbody fusion device 164 can then be positionedat a second bi-lateral location in the disc space. First and seconddevices 162, 164 provide bilateral support of the adjacent vertebrae,and can be packed with bone growth material G.

In some instances, the preparatory steps involve preparing the vertebralendplates by reducing the endplates to bleeding bone. In this instance,some aspiration and irrigation may be beneficial. The above procedurescan be conducted by tools and instruments extending through workingchannel cannula 20 and under direct vision from endoscope assembly 30.Graft material may also be placed directly in the prepared bore in thedisc space, either without any interbody fusion device or packed aroundthe inserted devices. This graft material can also be passed through theworking channel cannula 20 into the disc space location.

While the invention has been illustrated and described in detail in thedrawings and the foregoing description, the same is considered to beillustrative and not restrictive in character. It is understood thatonly the preferred embodiments have been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected.

1. A method for inserting at least one interbody fusion device in a discspace comprising a single cavity between adjacent vertebrae, comprising:creating a working channel to the disc space by placing a cannulathrough the skin and tissue of a patient using a transforaminal approachto the disc space; preparing the disc space through the working channelfor bi-lateral placement of the at least one interbody fusion device,wherein preparing the disc space includes inserting a chisel through thecannula and into the disc space, the chisel including upper and lowercutting edges to remove a portion of the vertebral endplates and acurved shaft defining a curvilinear cutting path, wherein preparing thedisc space includes inserting the curved shaft of the chisel into thecannula and moving the upper and lower cutting edges along vertebralendplates to prepare a cavity extending bilaterally across the adjacentvertebrae to receive the at least one interbody fusion device; andinserting the at least one interbody fusion device into the disc spacethrough the working channel so that the adjacent vertebrae arebi-laterally supported by the at least one interbody fusion device. 2.The method according to claim 1, further comprising inserting a viewingelement through the working channel; and preparing the disc spaceincludes preparing the disc space with the viewing element in theworking channel.
 3. The method according to claim 2, wherein insertingthe viewing element includes inserting the viewing element into theworking channel to directly visualize the disc space.
 4. The methodaccording to claim 1, wherein creating a working channel includes:inserting a first dilator through the skin and tissue of the patient;sequentially inserting at least one more dilator over the first dilator;inserting the cannula over the last inserted dilator; and removing thedilators so that the cannula defines the working channel.
 5. The methodaccording to claim 4, further comprising connecting the cannula to atable based arm.
 6. The method according to claim 1, wherein insertingat least one interbody fusion device comprises inserting a first fusiondevice through the cannula at a first bi-lateral location in the discspace opposite the cannula and inserting a second interbody fusiondevice through the cannula at a second bi-lateral location in the discspace adjacent the cannula.
 7. The method according to claim 1, whereinpreparing the disc space includes inserting a chisel in the disc space,the chisel having upper and lower cutting edges to remove a portion ofthe vertebral endplates.
 8. The method according to claim 7, wherein thechisel has a curved shaft defining a curvilinear cutting path.
 9. Themethod according to claim 1, wherein preparing the disc space includesinserting a shim through the working channel to maintain distraction ofthe disc space.
 10. A method for inserting at least one interbody fusiondevice in a disc space comprising a single cavity between adjacentvertebrae, comprising: creating a working channel to the disc space byplacing a cannula through the skin and tissue of a patient using aunitary transforaminal approach to the disc space; preparing the discspace through the working channel for bi-lateral placement of the atleast one interbody fusion device, wherein preparing the disc spaceincludes inserting a chisel through the cannula and into the disc space,the chisel including upper and lower cutting edges to remove a portionof the vertebral endplates and a curved shaft defining a curvilinearcutting path, wherein preparing the disc space includes inserting thecurved shaft of the chisel into the cannula and moving the upper andlower cutting edges along vertebral end plates to prepare a cavityextending bilaterally across the adjacent vertebrae to receive the atleast one interbody fusion device; and inserting at least one interbodyfusion device into the disc space through the working channel along theunitary transforaminal approach so that the at least one interbodyfusion device is positioned bi-laterally in the disc space to supportthe adjacent vertebrae.
 11. The method according to claim 10, furthercomprising inserting a viewing element through the working channel; andpreparing the disc space includes preparing the disc space with theviewing element in the working channel.
 12. The method according toclaim 11, wherein inserting the viewing element includes inserting theviewing element into the working channel to directly visualize the discspace.
 13. The method according to claim 11, wherein creating a workingchannel includes: inserting a first dilator through the skin and tissueof the patient; sequentially inserting at least one more dilator overthe first dilator; inserting the cannula over the last inserted dilator;and removing the dilators so that the cannula defines the workingchannel.
 14. The method according to claim 13, further comprisingconnecting the cannula to a table based arm.
 15. The method according toclaim 10, wherein inserting at least one interbody fusion devicecomprises inserting a first interbody fusion device through the cannulaat a first bi-lateral location in the disc space opposite the cannulaand inserting a second interbody fusion device through the cannula at asecond bi-lateral location in the disc space adjacent the cannula. 16.The method according to claim 10, wherein preparing the disc spaceincludes inserting a chisel in the disc space, the chisel having upperand lower cutting edges to remove a portion of the vertebral endplates.17. The method according to claim 16, wherein the chisel has a curvedshaft defining a curvilinear cutting path.
 18. The method according toclaim 10, wherein preparing the disc space includes inserting a shimthrough the working channel to maintain distraction of the disc space.